python---二叉树广度优先和深度优先遍历的实现

class Node(object):
    """结点"""
    def __init__(self, data):
        self.data = data
        self.lchild = None
        self.rchild = None
class BinaryTree(object):
    """二叉树"""
    def __init__(self, node=None):
        self.root = node
    def is_empty(self):
        """判断是否为空树"""
        return self.root is None
    def add(self, item):
        """在树的最后添加结点"""
        # 要添加的结点
        node = Node(item)
        # 空树
        if self.root is None:
            self.root = node
            return
        # 存放结点的队列, 从根结点开始
        queue = [self.root]
        while queue:
            cur_node = queue.pop(0)
            # 根结点的左孩子为空, 直接添加
            if cur_node.lchild is None:
                cur_node.lchild = node
                return
            # 根结点的左孩子不为空, 添加到结点队列
            else:
                queue.append(cur_node.lchild)
            # 根结点的右孩子为空, 直接添加
            if cur_node.rchild is None:
                cur_node.rchild = node
                return
            # 根结点的右孩子不为空, 添加到结点队列
            else:
                queue.append(cur_node.rchild)
    def breadth_travel(self):
        """广度优先遍历"""
        if self.root is None:
            return
        # 存放树结点的队列
        queue = [self.root]
        # 左右孩子均不为空,不进队列, 只弹出结点, 队列为空时结束
        while queue:
            # 弹出当前结点
            cur_node = queue.pop(0)
            print(cur_node.data, end=" ")
            # 左孩子不为空, 进队列
            if cur_node.lchild is not None:
                queue.append(cur_node.lchild)
            # 右孩子不为空, 进队列
            if cur_node.rchild is not None:
                queue.append(cur_node.rchild)
    def pre_order(self, node):
        """前序遍历, 根左右"""
        if node is None:
            return
        print(node.data, end=" ")
        self.pre_order(node.lchild)
        self.pre_order(node.rchild)
    def in_order(self, node):
        """中序遍历, 左根右"""
        if node is None:
            return
        self.in_order(node.lchild)
        print(node.data, end=" ")
        self.in_order(node.rchild)
    def post_order(self, node):
        """后序遍历, 左右根"""
        if node is None:
            return
        self.post_order(node.lchild)
        self.post_order(node.rchild)
        print(node.data, end=" ")
if __name__ == '__main__':
    tree = BinaryTree()
    print(tree.is_empty())
    tree.add(0)
    tree.add(1)
    tree.add(2)
    tree.add(3)
    tree.add(4)
    tree.add(5)
    tree.add(6)
    tree.add(7)
    tree.add(8)
    tree.add(9)
    tree.breadth_travel()      # 0 1 2 3 4 5 6 7 8 9
    print()
    tree.pre_order(tree.root)   # 0 1 3 7 8 4 9 2 5 6
    print()
    tree.in_order(tree.root)    # 7 3 8 1 9 4 0 5 2 6
    print()
    tree.post_order(tree.root)  # 7 8 3 9 4 1 5 6 2 0
    print()